Towing the Line
Tony Vasko ruminates on the evolution of towing equipment
By Tony Vasko
Moving aircraft is one of those routine airport jobs that seems simple but requires care and some planning to safely accomplish. Looking from the terminal, you can see the pilots steering their aircraft in and out of the gates with only one person on the ground to wave wands at them. Easily overlooked are the wing and tail walkers where the ramp is tight. Aircraft are awkward on the ground, at least most jets are, and their wings and tails reach out — eager to make contact with other aircraft or light poles or solid terminal buildings. These lead to some very expensive and time consuming out-of-service events.
ALL MAKES AND MODELS
Taxiing under engine power would seem to be the easiest way to move an aircraft, but it's not. You burn a lot of fuel, eat up some precious engine life and blow a lot of equipment about in the jet or prop blast. So towing is the preferred method. Here you ran into the problem of non-standardization. Each aircraft manufacturer had its own ideas on how to couple a tractor to its aircraft - although there has been some improvement in this and some standardization of head design has taken place.
For airlines, this non-standardization is a pain. They have to buy tow bars specific to the aircraft type(s) they are operating. For FBOs and ground handlers servicing many airlines, it can be a dreadful problem.
HOOKS, CLAWS, PINS, AND GRABBERS
In the 1950s, Lockheed Air Service in New York was the FBO of sorts for Idlewild Airport. It had originally been Willis Rose Aviation out on Long Island. The move to Idlewild came with an inherited horde of ironmongery comprised of a selection of aircraft towbars embracing both past and present types that filled a small storage yard. Some were long steel trusses while others were steel pipe. Some were very short, others very long. All had an eye on one end but the other ends were a bewildering array of hooks, claws, pins, and grabbers of every description. Some had hydraulic pumps and pistons to raise or lower the wheels; others had lever-type mechanisms, while still others had worm gears and wheels.
I had rapidly become familiar with the common variety of towbars that we used every day. The DC-4, DC-6, and DC-7 all used the same "through the nose wheel axle" attachment type of bar. It was fairly stubby and light and didn't need any fancy hydraulic or screw-jack systems to raise and lower it. The Constellations used attachment lugs on the nose gear itself. These required more precise aligning and the towbar was much more complicated. Most modern jets use the same type.
There were some very impressive models that looked like, and were the same size as, the boom from a crane. These were for tail dragger types like the C-46, the DC-3, and the Lockheed Lodestars. They had to be very long to go under the fuselage and hook on the tailwheel, yet still provide clearance for the tug to work around the elevators. Being of steel truss construction, they were also quite heavy. Humping them into place could be a job, particularly with snow and ice on the ground. There was one very rusty, but still impressive, towbar in that yard that I was assured was for the B-17. I never got to try it on one.
Truly the most impressive towbar I have ever seen belongs to the Russian AN-125. With two nose gears to contend with, it has two long girder sections vee-ing out behind the tug. These "tramp steamers of the sky" go anywhere, anytime, but they have to carry their bar with them, as AN-125 towbars are not common stock at most airports. It would take up a good part of the freight hold except they cleverly designed it to fold. Even so, it makes a unique package but is a very competent piece of engineering. I saw it in use in Tijuana, Mexico where two AN-125s were hauling out 100-ton loads of grapes destined for European tables.
Most towbars are fitted with shear pins for good reason. Tugs are powerful and aircraft sometimes refuse to move. If you try hard enough you can badly damage the nose gear by pulling too hard. The shear pin is designed to let go, hopefully, before the nose gear comes out by the roots. All well and good if this happens when you are just starting to move. You merely look silly driving away with a short piece of towbar attached. Not so good if you are in transit from the hangar to the gate and it shears as you are crossing runway 25L with the tower asking you to expedite as there is a B747 turning on to final.
When the pin shears, it releases the aircraft. It is very disconcerting for the tug driver to be moving along and realize that the airplane is no longer attached to his tug - especially if it catches up with him. It is even more disconcerting for the mechanic riding the brakes upstairs in the cockpit as he looks out and sees the tug going left while he and his airplane are not. Even more fun occurs if the hydraulic accumulator has gone flat, leaving him with a hand pump to work to build up pressure. This was in pre-APU days, of course. The old piston aircraft weren't blessed with them nor were the first generation jets. And, they didn't even have hand pumps - only the emergency air brakes.
There appears to be a better way now. Way back when, we used a "rocket launcher" to get Electras into Hangar 9 at Idlewild. The tail was slightly taller than the doors so the big scoop of the rocket launcher was backed into the nose wheels to scoop them off the ground. A bar was installed behind the wheels to hold them in place and an electric pump raised the scoop up about five feet. The tail went down and the rocket launcher with its captive Electra was towed into the hangar. It was then lowered as there was plenty of room for the tail inside.
The present day "towbarless" tractors work on the same principle except that they don't have to raise the airplane. I like the concept except it came along a bit late to help me. No humping a heavy bar up onto the nose gear lugs or fighting to make a lock mechanism engage. No straining to lift the eye end of the towbar up while directing a tractor driver to back up to engage the hook. No shear pin letting go at the wrong time. Best of all, no running around looking for the right towbar.
This equipment may not mean the elimination of the towbar but for certain applications, the towbarless tractor fits the bill.
Whether it's a towbar or towbarless method you use, it's important to be aware of your environment and to know both your limitations and those of the equipment when towing the line.